In a statement, the company said the violence broke out in the evening when a worker beat up a supervisor on the shop floor. However, the employees union said "objectionable remarks" by the supervisor against an employee triggered the violence.

"Work at the Manesar plant had to be stopped following the violence," the company said.

Labour unrest is not a new phenomenon in Manesar plant which mainly produces Swift. The factory had witnessed three such instances last year causing a total production loss of about 83,000 units.

"Workers at the plant today turned violent, attacking and injuring executives and managers in the office premises. At least 40 managers and executives are injured, and have been rushed to hospital. The attackers also set fire to property and damaged facilities," Maruti said.

"The sequence of events began in the morning with a worker beating up a supervisor on the shop floor. The workers' union prevented the management from taking disciplinary action against the worker," the company said.

As part of their protest, the workers prevented executives and managers from leaving the factory after working hours. They blocked the exit gates and held the executives hostage, it said.

Maruti said to resolve the issue amicably, members of the senior management met the union. During the talks, the workers attacked the members of the senior management, executives and managers, it alleged. This version was contested by the union.

Sarabjeet Singh, general secretary of the Maruti Suzuki Workers' Union (MSWU), said, "the supervisor made castiest remark against a permanent worker, who belongs to the Scheduled Caste category. When we opposed it, they misbehaved with us and suspended the worker".

"There is tension prevailing at the plant. About 1,500 workers of the morning shift have not left the complex. If the management does not take back the worker, we may stop our work," he said.